Tests of long wavelength infrared (LWIR) detectors require a low temperature, low photon operating environment. The detectors are sensitive to extraneous ionizing radiation effects typically associated with single radiation pulses, persistent dose rate noise, and total dose degradation. Testing for these effects is complicated by the operating environment in which these types of detectors must be evaluated. For example, testing for persistent dose rate noise (gamma noise) is typically done by exposing detectors housed in cryogenic chambers to Cobalt-60 gamma radiation. The difficulty with this approach is that Compton electrons penetrate the sample volume with variable energies and trajectories because of random origin and scattering, producing a poorly characterized ionizing environment. Data resulting from tests conducted in such environments must be interpreted in terms of these random excitations which cause considerable uncertainty in evaluating the experimental data. Total dose testing can also be accomplished using Cobalt-60 cells. However, large radiation sources are generally required to obtain significant doses in a reasonable time. Selective dosing of samples or devices is not possible with this approach.
The scanning electron microscope (SEM) is a powerful tool for investigating the effects of ionizing radiation because the electron beam energy, propagated beam location, illuminated area, beam intensity (effective dose rate) and beam pulse time can be easily controlled. However, room temperature infrared radiation is too intense to allow testing of infrared detectors with a scanning electron microscope by conventional methods. In order to reduce or eliminate background infrared radiation noise, the infrared detector must be tested in a cryogenic environment. Therefore, a need exists for an apparatus which could provide SEM probing and radiation simulation to an infrared detector shielded within a cryogenic shield.